(1) Field of the Invention
This invention relates to a method of fabrication used for semiconductor integrated circuit devices, and more specifically to an improved method of post-metal etch stripping of a photoresist mask and removal of residual corrosion inducing components.
(2) Description of Related Art
In the fabrication of semiconductor integrated circuits metal conductor lines are used to interconnect the many components in device circuits. Due to shrinkage in size of semiconductor components and increased circuit density, the complexity of interconnecting the many components in the dense circuits requires that the fabrication processes used to define the metal interconnect patterns provide precise dimensional control. Advances in lithography and masking techniques and dry etching processes, such as RIE (Reactive Ion Etching) and other plasma etching processes, allow production of sub-micron width conducting patterns with spacings also in the sub-micron range. In general, as illustrated in FIG. 1, the process steps used to pattern metal conductor patterns comprise: Step 10, deposition of a conducting layer; Step 11, formation by standard lithographic techniques of a photoresist mask or other mask, such as titanium oxide, silicon oxide or silicon oxynitride, in the form of the desired metal interconnection pattern; Step 12, loading the substrate to an etch tool; Step 13, dry etching to remove the conducting layer from areas not covered by the mask; Step 14, transferring the substrate to a photoresist strip chamber; Step 15, removing the photoresist mask layer, exposing the top surface of the metal layer; and then, Step 16, unloading the substrate from the etch tool.
As is well known in the industry, dry etching processes for metal layers composed of aluminum or aluminum alloys use chlorine and chlorine compounds as reactive components in the etchant gas. During the etching process the chlorine and chlorine compounds, as well as chlorine bearing reaction products, become embedded in and/or attached to the masked pattern sidewalls and other surfaces on the substrate. For example, chlorine and chlorine compounds and chlorine bearing reaction products become embedded into the photoresist mask on top of the etched metal pattern and attached to the sidewalls of the etched pattern. If the chlorine, chlorine compounds, and chlorine bearing reaction products are not removed or passivated before the substrate is exposed to the atmosphere of the manufacturing plant, then the residual chlorine causes corrosion and attack of the etched metal pattern. This corrosion is unacceptable, thereby reducing the yield of the metal etch process. Additionally, if the corrosion is not immediately detected, it will show up later as a cause for a device failure or as a contributing factor in a reliability failure mechanism. Therefore, it is extremely important that following a metal etch process the residual chlorine, chlorine compounds, and chlorine bearing reaction products be removed from all surfaces of the substrate and sidewalls of the etched metal pattern. The challenge in the industry is to provide post-metal etch processes which efficiently and effectively strip the photoresist mask and, also, remove residual chlorine, chlorine compounds, and chlorine bearing reaction products.
It is a well known fact that O.sub.2 can be used to remove or etch photoresist, as shown in U.S. Pat. No. 4, 732,658 entitled "Planarization Of Silicon Semiconductor Devices" granted Mar. 22, 1988 to Eddie C. Lee, which shows a dielectric planarization process in which a photoresist layer is deposited over a dielectric layer having topographical features and then etching back all of the photoresist and enough of the dielectric layer to form a substantially planar surface of the dielectric material. The etchback process, using CHF.sub.3 and O.sub.2, etches photoresist and the dielectric at substantially the same rate. However, this patent does not address the removal of chlorine, chlorine compounds, or chlorine bearing reaction products following dry etching of an aluminum interconnection pattern.
U.S. Pat. No. 5,792,672 entitled "Photoresist Strip Method" granted Aug. 11, 1998 to Lap Chan et al. describes a two step photoresist strip method in which after etching a conducting material the substrate containing the etched pattern is transferred to a second heated chamber and the photoresist is stripped first in a plasma containing O.sub.2 and H.sub.2 O and second in a plasma containing O.sub.2. While this process offers an improvement to state-of-the-art photoresist stripping, there continues to remain a challenge to devise effective methods to strip photoresist masks from etched aluminum or aluminum-copper interconnection patterns subsequent to etching the pattern in a chlorine containing plasma and to remove chlorine, chlorine compounds, or chlorine bearing reaction products following the dry etching of the aluminum or aluminum-copper interconnection pattern.
U.S. Pat. No. 5,824,604 entitled "Hydrocarbon-Enhanced Dry Stripping Of Photoresist" granted Oct. 20, 1998 to Ronny Bar-Gadda describes a method of stripping photoresist using a microwave stripper and a plasma containing an oxidizing gas, a fluoride-containing compound, and a hydrocarbon-containing reactive species.
The present invention is directed to a novel method of stripping a photoresist mask from the surface of an aluminum or aluminum-copper pattern formed by dry etching processes using gaseous Cl.sub.2 and BCl.sub.3 etchants by using alternating steps for passivation and photoresist stripping which sequentially passivate the etched aluminum or aluminum-copper surfaces and remove the photoresist. Superior results are obtained using a five step process which combines passivation and photo-resist stripping in Step 1, followed by photoresist stripping in Step 2, followed by passivation in Step 3, followed by photoresist stripping in Step 4, followed by passivation in Step 5.